As compared with a traditional cathode ray tube display device, a flat panel display device has advantages such as lightness and thinness, low driving voltage, no flicker and jitter and a long service life. The flat panel display device is divided into an active light-emitting display device and a passive light-emitting display device; for example, a thin film transistor-liquid crystal display (TFT-LCD) is the passive light-emitting display device, and is widely applied to an electronic product such as a television, a mobile phone and a monitor, due to advantages such as stable picture, realistic image, low radiation, space saving and energy saving, which has dominated a flat panel display field.
It has been known to the inventor that a liquid crystal display panel mainly includes a color filter substrate and an array substrate cell-assembled, and there is a liquid crystal layer interposed between the color filter substrate and the array substrate. Herein, a thickness of the liquid crystal layer (also known as a cell gap) is controlled mainly by a height of a spacer disposed between the array substrate and the color filter substrate, and the cell gap has important influence on structural parameters and display quality of the liquid crystal display device. The spacer used at present is generally a Post Spacer (PS), which is generally formed on a black matrix of the color filter substrate by a mask process, a photolithographic process and the like. The liquid crystal display panel is formed after cell-assembling the color filter substrate and the array substrate, and the PS located between the color filter substrate and the array substrate plays a role in supporting and buffering the above-described two substrates, so as to maintain a predetermined cell gap and ensure the stability of picture display.
Currently, a large-sized high-resolution television (such as a 65-inch ultra-HD television product, etc.) is increasingly favored by consumers. In a large-sized liquid crystal display panel, typically various different types of spacers are used to prevent a mura or a displaying defect. For example, FIG. 1 shows a cross-sectional view of a Triple PS known to the inventor, which includes a main spacer (main PS) 14, a first auxiliary spacer 15 and a second auxiliary spacer 16 disposed on the black matrix, and have a function of three-level buffering. Therein, the main spacer 14 is usually in a compressed state, with a main purpose to prevent occurrence of gravity Mura in the liquid crystal display panel. Here, the gravity Mura refers to that when the liquid crystal display panel is placed vertically, liquid crystal material will accumulate to a lower portion of the liquid crystal display panel by gravity, resulting in expansion of the lower portion of the liquid crystal display panel, while a vacuum occurs in an upper portion of the liquid crystal display panel; and under effect of external atmospheric pressure, the upper portion of the liquid crystal display panel is pressed, resulting in serious nonuniformity between cell gap of the upper portion and cell gap of the lower portion of the liquid crystal display panel, so as to cause unevenness in the picture display. In the large-sized liquid crystal display panel, since a large amount of liquid crystal is injected, the gravity Mura is more apt to occur. The main spacer 14 is usually disposed in the upper portion of the liquid crystal display panel, and prevents the occurrence of the gravity Mura through its own elasticity, when the liquid crystal display panel is placed vertically. Therefore, a compression amount of the main spacer 14 has significant correlation with an upper limit of the liquid crystal amount injected into the liquid crystal display panel and an ability to prevent the gravity Mura. Simply put, the larger the compression amount of the main spacer 14, the more the pressure it can withstand so as to maintain the cell gap unchanged, and the less likely the gravity Mura will occur, and correspondingly, the more liquid crystal material can be injected, so as to enhance a picture display effect.
Since the spacer is usually formed on the color filter substrate, as shown in FIG. 2, in order to further increase the compression amount of the main spacer 14, typically an auxiliary pillow layer 24 is formed by using functional film layers 23 on the array substrate, the main spacer 14 is in contact with the auxiliary pillow layer 24 by pressing, and the compression amount of the main spacer 14 is increased by using the auxiliary pillow layer 24. However, since a thickness of the auxiliary pillow layer 24 is determined by thicknesses of the functional film layers 23 on the array substrate, for example, when the auxiliary pillow layer is disposed in a same layer with a gate metal layer, the thickness of the auxiliary pillow layer is equal to a thickness of the gate metal layer, and when the auxiliary pillow layer is disposed in a same layer with a passivation layer, the thickness of the auxiliary pillow layer is equal to a thickness of the passivation layer; while the thicknesses of each of the functional film layers on the array substrate are all fixed values, which cannot be changed arbitrarily, and thus the thickness of the auxiliary pillow layer 24 cannot be changed continuously, i.e., only some specific compression amounts can be satisfied, but it is hard to meet requirements of various changed compression amounts. Besides, in principle, the continuous change of the compression amount can also be achieved by continuous change of a height of the spacer per se; but in fact, the height of the spacer is determined by a diameter of the spacer; once the diameter of the spacer is determined according to a space on the array substrate and a size parameter of the black matrix, it means that the height of the spacer can be changed only within a short range, so the continuous change of the compression amount cannot be truly achieved, either, i.e., it is impossible to meet the requirements of various changed compression amounts.
In addition, in the pursuit of the large-screen ultra-HD product, it is bound to bring an increase in power consumption of the display panel, which is in conflict with an energy-saving and low-carbon concept of environmental protection. In an oxide-semiconductor thin film transistor (Oxide-TFT) driving technology, since an oxide semiconductor has a relatively high electron mobility (about 100 times faster than that of a conventional amorphous silicon), the power consumption of the liquid crystal display panel can be greatly reduced, which thus has unparalleled technical advantages in the large-sized liquid crystal display products, and is rated as a new generation of liquid crystal display technology which is the most promising, and has a good market prospect. However, in the Oxide-semiconductor-TFT liquid crystal display panel, as compared with the conventional liquid crystal display panel with the amorphous silicon thin film transistor, a thickness of a functional film layer formed by the oxide semiconductor is very small, which is typically 0.05 μm, far less than a thickness of a functional film layer formed by the conventional amorphous silicon (typically 0.23 μm); and thereby, although a thickness of the array substrate is reduced, yet the compression amount of the main spacer is also reduced by nearly 10% (a ratio of the compression amount to an original height thereof); typically, the compression amount of the main spacer is, only about 15% at most (the ratio of the compression amount to the original height thereof), but an insufficient compression amount of the main spacer is bound to result in the occurrence of the gravity Mura; since the thickness of the auxiliary pillow layer is relatively fixed, it is necessary to increase the height of the spacer, and but, an increase in the height of the spacer means necessity to increase the diameter of the spacer, so that the material cost is greatly increased. In addition, limited by the space on the array substrate and the size parameter of the black matrix, the diameter and the height of the spacer are not infinitely changeable at all. All these factors limit design of the spacer, so that the compression amount of the Oxide-TFT liquid crystal display panel is relatively small, and there is a risk of the gravity Mura, meanwhile problems such as increase of the material cost of the spacer and reduction of production capacity will also be caused.